Manufacture of substituted pyrroles



Patented Aug..14,. 1945 Maurice Arthur l m calllndustries' imit Britain No-Drawingi rial NoI457 2.194 1...

The inventionrel ates to the manufacture of newconipounds, namely, 2-:4- diary1pyrroles'. i

It is known that pyrrolines and pyrrolidines TU'IfED ed, a corporation of Great...

are dehydrogenated bysuitable heat treatment in the presence of precious metal catalysts.

According to the present invention Iprovide a process for the manufacture of 2':4=-diarylpyrroles which comprises bringing a 2:4-diarylpyrroline or a, 2:4-diarylpyrrolidine into contact, in the liquid phase, with a dehydrogenation agent at a suitable temperature for dehydrogenation.

The new 2:4-diarylpyrroles have the formula [I Ar-C.

wherein Ar and Ar each stand for aryl radicals, for example of the benzene ornaphthalene series, the same 'or different, substituted or not.

The starting-out materials, namely, the 2:4- diarylpyrrolines and -pyrrolidines, are obtainable by reduction ofcompounds of the general formula AIECIIIICHQCOAY" Q wherein Ar and Ar stand for aryl radicalsand Application September 3,1942 Se-' Great Britain December (17,

hydrogenationof thepyrroline orpyrrolidine may 3 be brought about in Such away that the hydrogen combines with the sulphur to give hydrogen sulphide. In this connection it is noteworthy that, contrary to what might be supposed from the known behaviour of selenium in dehydrogenating other compounds, we have found that in the process of the present invention it acts catalytically, that is to say, the dehydrogenation which takes place in presence of selenium does not involve the formation of hydrogen selenide, or at least, the greater part of the selenium has acted catalytically in the sense that it is recoverable unchanged at the end of the process.

As a convenient temperature at which to carry out the dehydrogenation process the range of from 250 to 360 C. has been found suitable. To obviate any action of the oxygen of the air,

. the process may be carried out in an inert atmos- X stands for the group CH2NO2 or the group CN. Thus 2:4-dipheny1pyrroline may be-made by reduction of. 1-nitro-Z:4-diphenylbutanone-4 by means of zinc dust or iron filings and acetic acid (Sonn, Berichte der deutschen Chemischen Gesellschaft, 1935, vol. 68, page 148) orby reduction of 1-pheny1-2-benz0yl-propionitri1e by means of hydrogen in presence of a nickel catalyst (Rupe and Gisiger,

vol. 8, page 338).

As examples of starting-out materials there may be mentioned 2:4-dipheny1pyrroline, .2-(p- I-I elvetica v Chimica Acta 1925,

methoxyphenyl) -4-phenylpyrroline, 2-phenyl-4 (p-methoxylphenyl) pyrroline, 2 -(m-hydroxyphenyl) -4-pheny1pyrroline, 2-(o-chlorophenyl) l-phenylpyrroline, 2 (p-acetylaminophenyl) -4- phenylpyrroline, 2-a-naphthyl-4-phenylpyrroline, 2-phenyl-4 p-naphthylpyrroline, or the corresponding pyrrolidines.

phere, forexample, in an atmosphere of nitrogen. After the completion of the dehydrogenation process the reaction mixture is cooled and separated from the dehydrogenation agent, as by solution in a suitable liquid, for example benzene or chloroform, followed by filtration. The pyrrole may be recovered from the filtered solution by, for example, evaporation, and may thereafter be purified by conventional methods.

The new compounds are useful as intermediates. i

The following examp1es,in which the parts are .byweightQillustrate but do not limit the inven tion: v

Example 1 5 parts of 2:4-diphenylpyrroline are mixed with 5 parts of powdered selenium in a vessel adapted for the passage of a current of nitrogen. Nitrogen is passedthrough the vessel and the contents are heated to 250 C. for 3 hours. The

reaction mixture is then cooled and 25 parts of hot benzene are added. This mixture is filtered.

As suitable dehydrogenation agents, there may 3 be mentioned selenium, Raney. nickel (see U. S. P. 1,628,190), molybdenum sulphide, copper chromite, copper powder, zinc dust, and sulphur. These do not necessarily all behave in the same way in effecting the dehydrogenation. Some, as for example Raney nickel act catalytically, that is to say the agent is recoverable unchanged at the end of the process. catalytically, for example with sulphur the dc Others may not act The 2:4-diphenylpyrrole separates from the benzene on cooling in long, colourless needles, M. P. 179-180 C.

, ExampleZ 10 parts of 2:4-diphenylpyrroline are heated in a vessel fitted for the passage of nitrogern with one part of Raney nickel. Nitrogen is passed through the vessel. and the contents are heated at 360 Cxfor 6 hours. The mixture'is then cooled and parts of hot chloroformare added. The solution is then filtered to remove nickel and the filtrate is concentrated by dis- FFICE 1 tillation until 30 parts of chloroform have distilled. The residual solution when cooled deposits crystals of 2:4-dipheny1pyrrole.

Iclaimz v 1. 2:4-diarylpyrro1es of the formula I which comprises heating 2:4-diphenylpyrro1ine in the liquid phase, in an inert atmosphere and in contact with selenium at a temperature of about 250 C., -and recovering the reaction product. t

wherein Ar and Ar stand for aryl radicals oi" (10":

5. A process of preparing 2:4'-diphenylpyrrole, which comprises heating 2:4-diphenylpyrroline in the liquid phase, in an inert atmosphere and in contact with a nickel dehydrogenation catalyst, at a temperature of about 360 C., and recovering the reaction product.

6. A process for the manufacture of 2:4-

' diaryl-pyrroles having the formula wherein Ar and Ar stand for aryl radicals of the benzene series, which comprises bringing member of the group consisting of the corresponding 2:4-diary1-pyrrolines and 2:4-diary1- pyrrolidines into contact, in the liquid phase, with a. dehydrogenation agent, at a temperature within the range of 250 to 360 C.

MAURICE ARTHUR THOROLD ROGERS. v

CERTIFICATE OF CORRECTION.

Patent No. 2,382,915. August 1t, 1915.

MAURICE ARTHUR THOROLD ROGERS.

It is hereby certified that error appears in the printed specification of the above numbered pateht requiring correction as follows: Page 1, first column, line 1 0, for p-methoxylphenyl)-pyrroline read --(p-methoxyphenyl)- pyrroline-; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of November, A. D. 1914.5,

Leslie Frazer (Seal) First Assistant Commissioner of Patents. 

